Remote control system



y 1939. L. L. CUNNINGHAM 2,160,400

REMOTE CONTROL SYSTEM Filed May 27, 1933 9 Sheets-Sheet 1 INVENTOR LEWISL.. CUNNINGHAM ATTORNEYS y 30, 1939- L. CUNNINGHAM 2,160,400

REMOTE CONTROL SYSTEM Filed May'27, 1935 9 SheetsSheet 2 INVENTOH LEWISL.CUNNIN6HAM A 'rromvEYs' y 1939- L. L. CUNNINGHAM 2,160,400

REIOTE CONTROL SYSTEM Filed lay 27, 1935 9 Sheets-Sheet s IN VENTORLEWIS LfiUNNINGHAM A TTORNEYS y 1939- L. L. CUNNINGHAM REMOTE CONTROLSYSTEM Filed May 27, 1933 9 Sheets-Sheet 4 I'NVENTOR Lew/s L. CUNNINGHAMWM I /*4 ATTORNEY y 1939- L. CUNNINGHAM 2 ,160,400

REMOTE CONTROL SYSTEM Filed May 27, 1933 9 Sheet s-Shee t 6 INvENToRLEWIS L. Cu NINGHAM v m Mil/M A r-romvzys May 30, 1939.

L. L. CUNNINGHAM REMOTE CONTROL SYSTEM Filed May 27, 1933 9 Sheets-Sheet8 /,v V/f/VTUR LEW/5 L.. CUNNINGHAM May 30, 1939.

L. LTCUNNINGHAM REMOTE CONTROL SYSTEM Filed May 27, 1955 9 Sheets-Sheet9 INVENTOR LEWIS L. CUNNINGHAM A TTORNEYS Patented May 3Q, 1939 UNITEDSTATES PATENT OFFICE REMOTE CONTROL SYSTEM Delaware Application May 27,1933, Serial No. 673,236

14 Claims.

The present invention relates to an electrical transmission or controlsystem by which the movement of a member which is relatively sensitiveor develops a small amount of power may be transmitted to aninstrumentality which it is desired to control or move in accordancewith the movement of said member.

' Systems of this general type have been heretofore'proposed in which amovable member moved one of a pair of co-operable electrical contactstoward or away from engagement with the other of the pair 01' contacts,the contacts, when enga ed, completing an electrical circuit to anelectrically controlled device which, upon energiza- 15 tion, movedthesecond contact away from the first contact to break the circuit whichmay have been formerly established by engagement of the contacts and atthe same time positioned an instrumentality in accordance with thatposition of the movable member which resulted in the movement of thefirst contact toward or away from the second contact.

Such prior art systems are fairly satisfactory for certain classes ofwork but lack the necessary flexibility to permit their adaptation toall classes of work. For example, the electrically controlled device hasbeen directly mechanically connected to one of the pair of contacts, inorder I to cause their separation after the instrumental? ity has beenmoved to a position corresponding to the position of the movable member.In many instances, the electrically controlled device must be mountedupon a machine or other object which is subject'to vibration, and thesevibrations are transmitted to threlectrically controlled device and inturn to that one of the pair of contacts controlled thereby, thuscausing the pair of contacts to chatter whereby the operation of thesystem is rendered unsatisfactory.

It is a broad purpose of this invention to provide an improved form ofelectrical system for transmitting the movements of a delicate orsensitive member wherein the controlled device is mechanically remotefrom the contacts opened and closed by such sensitive member.

More particularly the present invention con- I the electricallycontrolled device when the instrumentality has been so moved. By thisarrangement, in which the switching mechanism is operated by theconjoint action of the movable member and the electrical meanscontrolled or operated by the electrically controlled device, theswitching mechanism may be placed remotely in respect to theelectrically controlled device whereby the switching mechanism is notsubject to disturbances, such as vibration, to which the electricallyoperated device may be subjected.

Again, a feature of the invention resides in the provision of a systemof the class described in which one contact of a pair of contacts ismoved toward or away from engagement with the other by a movable controlmember, and in which the contacts when in engagement energize anelectrically controlled device that positions a controlledinstrumentality inaccordance with the movable member, and also operatesthe first said contact to separate the pair upon such positioning. Theelectrically controlled device may be a reversible electric motor .or apair of electrical motors which are mechanically interconnected to actas a reversible electric motor. In such a case, the switching mechanismpreferably is of the double throw or double circuit type. On the otherhand, the electrically controlled device may be a single circuit device,such as a heat motor, in which case the switching mechanism would be ofthe single throw or single circuit type.

A further object of the invention is the provision of a system of theabove-mentioned type in which the electrically controlled device, suchas a reversible electric motor or heat motor operates electrical meanswhich in turn move thev same contact that is positioned by the movablemember to separate it from its cooperating contact.

A more specific object of the invention is the' provision of a systemembodying normally balanced electrically controlled means which areunbalanced and rebalanced by the conjoint action of a movable controlmember and an electrically controlled device, the energization of thelatter being controlled by a switching mechanism operated by thenormally balanced electrically controlled means. The electricallycontrolled device is thereby positioned in accordance with the positionof the movable member and in turn positions any desired instrumentalityin accordance with the position thereof.

More specifically, the invention contemplates balancing potentiometerswhich are electrically associated therewith, the control potentiometerbeing operated by a movable control member and the balancingpotentiometer being operated by an electrically controlled device andthe energization of the latter being controlled by a switching mechanismoperated by the normally balanced electrically controlled means.

It will be obvious, that the balanced electrically controlled means,such as a center-tapped solenoid, may be placed remotely in respect toeither the'movable member or the electrically controlled device or both.

Another object of the invention is the provisiornof means for'increasingthe contact pressure of one of a pair of contacts against the other in asystem of the above-described type. This is preferably accomplished byestablishing an auxilliary energizing circuit through a portion of thenormally balanced electrically controlled means or center-tappedsolenoid as the result of engagement of one of the contacts with theother whereby the contacts will be more firmly engaged untilsubsequently separated by the action of the electrically controlleddevice.

Systems of the above-described type are particularly adaptable tothecontrol of heating systems wherein the movable member is positioned byor in accordance with a temperature and/or pressure condition of aheating system and the controlled instrumentality controls the supply ofheat either directly or indirectly,'as by controlling the supply of fuelto a heater.

Still another object of the invention, there- 'fore, is the applicationof any of the abovedescribed systems to a heating system.

In the practical control of a heating system, for instance, it hassometimes been found that the positioning of a heat controlinstrumentality in accordance with the temperature and/or pressurecondition to be controlled permits of undesirable large fluctuationsfrom normal of the temperature and/or pressure condition if the demandor load on the heating system varies in a substantial amount. Underthese conditions it is desirable to primarily position the heat controlinstrumentality in accordance with the position of a movable memberresponding to the temperature and/or pressure condition and to alsochange the position of the heat control instrumentality in accordancewith the deviation of the movable member from its normal position and/orin accordance with the length of time that such deviation persists.

An additional object of the invention is the positioning of a controlinstrumentality primarily in accordance with the position of a movablemember and also in accordance with the deviation of that, or another,movable member from its normal desired position and/or in accordancewith the length oi! time that such abnormal deviation persists.

It is also often desirable to additionally change the position of theheat control instrumentality in respect to the position of a movablemember upon initial revers movement of the movable member. In otherwords, upon initial reverse movement of the-movable member, the heatcontrol instrumentality is given an initial movement in a direction tocheck or counter-act the change which caused such reverse movement of"the movable member. This initial change in position of the heat controlinstrumentality is in addition to the usual movements resulting from anymove- 1 ment of the movable member and may also be in addition to thecorrective movements applied as a result of a deviation of the movablemember from its desired normal positionin accordance with the amount ofsuch deviation and/or in accordance with the length of time suchdeviation persists.

An additional object oi. the invention is the positioning of a controlinstrumentality primarily in accordance with the position of a movablemember and also as a result of initial reverse movements of the movablemember.

Another object of the invention is the positioning of a controlinstrumentality primarily in accordance with the position of a movablemember and also in accordance with the deviation of that, or another,movable member from its normal desired position and/or in accordancewith the length of time that such abnormal 'deviation persists and, inaddition, to adjust the position of the control instrumentality uponinitial reverse movement of the movable member.

More specifically, the invention has for an object, the provision of asystem in which 2. normally balanced electrically controlled means isunbalanced by the movement of a movable mem-- her from its normaldesired position and is additionally unbalanced in proportion to theamount of deviation of the movable member from its normal desiredposition and/or in accordance with the length of time such deviationpersists and/or as a result of initial reverse movement of the movablemember. The system is such that the unbalancing of the normally balancedelectrically controlled means or balanced solenoid operates a switchingmechanism in control of an electrically controlled device whichpositions a control instrumentality in accordance with the degree 01'unbalancing of the electrically controlled means and also electricallyrebalances said means.

A further object of the invention is the unbalancing of a normallybalanced electrically controlled means by the cooperative action of aplurality of movable members, the unbalancing of the electricallycontrolled means in turn operating an electrically controlled devicewhich positions an instrumentality in accordance with the degree towhich said electrically controlled means has been unbalanced-and alsooperates electrical means to rebalance said electrically controlledmeans. This may be accomplished by having a plurality of movable membersoperate a like number of control potentiometers which are connected inseries, parallel, or series. parallel with the normally balancedelectrically controlled means and/or by having one or more or themovable memberscontrol variable resistances connected in circuit withone or more of the control potentiometers and normally balancedelectrically controlled means. device preferably controls a singlebalancing potentiometer which rebalances the normally balancedelectrically controlled means after the same has been unbalanced by thecooperation of the plurality of movablemembers.

A further object of the invention is the provision in any of theabove-mentioned systems, of

I a control means operated by the electrically controlled device wherebya second electrically controlled device may be controlled by theposition of the first electrically controlled device. In this manner afirst instrumentality may be positioned in accordance with the movementof one or more movable members and, ir'desired, by the amount ofdeviation of the movable members from their desired normal positions,and a second instru- The electrically controlled and the secondinstrumentality.

theother of which serves as the control potentio-.

meter for the second electrically operated device which operates its ownbalancing potentiometer Again, it is an object of the invention toprovide a control system for an electrically heated heating device inwhich an induction voltage regulator is controlled, or the movablewinding thereof is positioned, in accordance with a heater conditionwhereby the electromotive force impressed upon the electrical heatingelement or elements of the heating device is varied in accordance with aheater condition.

Another object of the invention is the provision of means whereby thesensitivity of the various systems may be adjusted so that apredetermined amount of movement of a movable member is required beforethe instrumentalityto be controlled is repositioned and/or so that themagnitude of the resulting movement of the instrumentality to becontrolled for a given movement of the movable member may be varied.

These and other objects of the invention will become apparent as thedescription thereof proceeds.

For a more complete understanding of the invention, reference may be hadto the following description and accompanying drawings, in which:

Fig. l is a longitudinal sectional view of a reversible motor assemblywhich operates a valve and a balancing potentiometer in accordance withone embodiment of the invention,

Fig. 2 is an end view of the apparatus of Fig. 1, looking from the leftwith the cover removed and omitting the valve structure,

Fig. 3 is a partial section taken about on line 33 of Fig. 1 and showingthe manner in which thelimit switches are operated,

Fig. 4 is a schematic view showing one complete embodiment of theinvention as applied to the apparatus of Fig. 1,

Fig. 5 is a side view, with parts in section, of a modified and improvedbalancing potentiometer and limit switch mechanism,

Fig. 6 is a top view of the balancing potentiometer and limit switchmechanism of Fig. 5,

Fig. 7 is a sectional view taken about on line 11 of Fig. 6,

Fig. 8 is a diagrammatic view similar to that of Fig. 4, in which aslightly modified embodiment of the invention is shown applied to themechanism of Figs. 6, '7, and 8, I

Fig. 9 is a diagrammatic view similar to that of Fig. 8 to which a loadcompensating mechanisin and other corrective mechanism has been added,

Fig. 10 is a diagrammatic view showing a few of the many manners inwhich the operation of the systems contemplated by the present inven--Referring first to Figs. 1, 2, and 3 a cylindrical casing indicated atis provided with a cover 2|. Housed within the casing are a pair' ofsquirrel cage induction shaded pole motors generally indicated at 22 and23. Motor 22 comprises a laminated field core 24, a field winding 25 anda squirrel cage rotor 26. Likewise, motor 23 comprises a laminated fieldcore 21, a field winding 28 and squirrel cage rotor 29. Both rotors 26and 29 are mounted on and secured to' a common shaft 30 journalled inbearings 3| and 32. The motors 22 and 23 are so arranged that their r0-tors rotate shaft 30 in opposite directions upon energization of theirrespective field windings 25 and 28 whereby the two motors 22 and 23,taken together, operate as a single reversible motor. Shaft 30 ismechanically connected to a second shaft 33 by means of a reduction geartrain generally indicated at 34 whereby the rotation of shaft 30 istransmitted to shaft 33 at a greatly reduced speed and with acorrespondingly greater torque.

The right hand end of shaft 33 extends beyond casing 26 and carries apinion 35 at its'extremity. Pinion 35 meshes with teeth 36 formed in avalve stem 31 which operates a valve generally indicated at 38. The lefthand end of shaft 33 terminates within casing 20 and is provided with aninternal longitudinal bore shown at 39. A fiber circular end plate 48supported by casing 20 journals bearing 3| and a bushing 4| while asimilar end plate 42 journals bearing 32. Bushing 4| journals 9. shortstud shaft 43, thereduced inner end 44 of which is received by the bore39 of shaft 33 and the end of shaft 33 isconnected to stud shaft 43 by anut 45 which presses the split end of shaft 33- against the periphery ofi the reduced end 44 of stud shaft 43.

' A fiber cylinder 46 is journaled on and secured to stud'shaft 43 bymeans of a screw 41. A pair of limit switch actuators 48 and 49 areadjustably secured to fiber cylinder 46 by means of screws 50 stationarycoiled resistance 54 over which the movable arm 52 is adapted to sweep.The ends of resistance 54 are secured to straps 55 and 56 which in turnare bolted to fiber end plate 40.

A. pair of limit switches include pivoted bell cranks 51 and 58. Arm 59of bell crank 51 .car-

ries a contact 60 which is normally in engagement with a stationarycontact 6| carried by a post 62 mounted on fiber end plate 48 and arm 53of bell crank 51 extends into the path of movement of the extended end64 of limit switch actuator 48. likewise, arm 55 of bell crank 58carries a contact which is normally-in engagement with a contact 61carried by a post 68 secured to fiber end plate 40 and arm 69 of bellcrank 58 extends into the path of movement of the extended end 10 oflimit switch actuator 49.

It will be evident that the motion of stud shaft 43 is transmitted tomovable arm 52 and limit switch actuators 58 and 51.

Now referring specifically to Fig. 4 of the drawings, a controlpotentiometer 1| comprises a control resistance 12 and a movable member13 which -is herein shown as operated by a bimetallic element 14. a Itshould be distinctly understood that the use of a bimetallic element inthis embodiment of the invention is only illustrative of one of thermanyways in which movable member 13 may be controlled. Movable member 13 mayrespond to any physical condition or may be moved by any desired forceor in any other desired manner. Normally balanced electrical means areherein shown as a balanced solenoid which comprises a singlecenter-tapped solenoid or which may be considered as two equal solenoidwindings 15 and 16. Solenoid windings 15 and 16 control a plunger 11which is connected to a flexible switch arm I8 by a light coiled spring19. One end of flexible switch arm 18 is secured as shown at 88. Theother end thereof carries a small armature M which cooperates withmagnet windings 82 and 83. A pair of movable contacts 84 and 85 are alsocarried by flexible switch arm 18 and cooperate with stationary contacts88 and 81 respectively. Contacts 88 and {81 are respectively connectedto one end-eachv of magnet windings 82 and 83.-

A relay comprises relay windings 88 and 89 which control a plunger 98that is connected to a flexible relay switch arm M by a light coilspring 92. Relay switch arm M is secured at one end as shown at 99 andits free end carries movable contacts 94 and 95 which cooperate withstationary contacts 96 and 91.

High voltage line wires 98 and 99 supply electrical power to the systemof Fig. 4 which includes a step-down transformer having a high voltageprimary I 88 connected to line wires 98 and 99. The low voltagesecondary is shown at I9I. ondary I8I with solenoid winding I5 and wiresI84 and I95 connect the other side of secondary I8I with solenoidwinding 16. Solenoid winding 15 is connected to one end of controlresistance 12 through a protective resistance I86 by wires I81 and I88and solenoid winding It is connected to the other end of controlresistance 12 through a protective resistance I89 by means of wires I I8and II I. One end of balancing resistance 54 is connected to one end ofcontrol resistance It by a wire 2 and the other ends of the balancingand control resistances are connected by a wire H3. Wires H4, H5, and H8interconnect balancing arm 52, movable member 18 and the junction ofsolenoid windings 15 and I6.

One side of secondary IN is connected to magnet winding 83 and relaywinding 88 by wires I84,

"1, and H8. The other side of secondary MI is connected to magnetwinding 82 and relay winding 89 by wires I82, II9, and I28. The junctionof relay windings 88 and 89 is connected to flexible switch arm 18through a protective resistance I2I.

One end of each of the motor field windings 25 and.28 is connected toline 99 by wires I22, I23, and I24. The other end of field winding 25 isconnected to contact 68 by a wire I25 and the other end of field winding28 is connected to contact 66 by a wire I26. Contacts 6| and 96 areconnected together by a wire I21 and contacts 61 and 91 are connectedtogether by a wire I28. Relay switcharm 9| is connected to line wire 98by a wire I29.

Operation of the system of Fig. 4

With the parts in the position of Fig.4, wherein the movable arm 52 iscontacting the center of balancing resistance 54 and the movablemember13 is contacting the center of control resistance 12, the voltage dropsacross solenoid windings 15 and 16 are equal and both of these solenoidwindings are equally energized by the secondary I8I. Plunger 11 istherefore maintained in a middle or center position wherein flexibleswitch arm 18 is in a normal unflexed position Wires I82 and I83 connectone side of secand movable contacts 84 and 85 are out of engagement withstationary contacts 86 and 81 respectively. Relay windings 88 and 89 aretherefore equally energized by the following circuit: secondary I8I,wire I82, wire 9, wire I28, relay windings 89 and 88, wire II8, wire H1,and wire I84 back to secondary I8I. Relay plunger 98 is thereforemaintained in a middle or center position whereby relay switch arm 9|assumes its center unflexed position wherein contacts 94 and 95 are outof engagement with their respective stationary contacts 96 and 91. Fieldwindings 25 and 28 are therefore both de-energized and the valve 38 is,for example, in a mid-position. It will be assumed for the purpose ofthis explanation that valve 38 controls the flow of a heating medium toa heating device or the flow of fuel to a burner to maintain a desiredtemperature in a space to which bimetallic element It responds. As longas this temperature remains at the desired point, bimetallic element 14will maintain movable member 13 in contact with the center of controlresistance 12 and all of the parts will remain in the position shown inFig. 4. Now, if the temperature should rise slightly, bimetallic element14 will move movable member I3 to the left along control resistance 12to a point corresponding to the new temperature condition to whichbimetallic element 14 is responding. This movement of movable member I8to the left along control resistance 12 changes the resistance in shuntwith solenoid windings 15 and 16 in such a manner that the voltage dropacross solenoid winding 15 is reduced and the voltage drop acrosssolenoid winding 16 is increased. Solenoid winding 16 is now energizedmore than solenoid winding 15 whereupon plunger 11 moves to the rightand moves flexible switch arm 18 in the same direction causing movablecontact 84 to engage stationary contact 86.

' A series circuit including magnet winding 82 and protective resistance|2| is thereby connected in parallel with relay winding 89 whereby thevoltage drop across relay winding 89 is decreased and the voltage dropacross relay winding 88 is increased whereupon plunger 98 is moved tothe left. Movement of plunger 98 to the left moves relay switch arm 9|to the left bringing movable contact 95 into engagement with stationarycontact 91. The current which flows through magnet winding 82 produces amagnetic flux which attracts armature 8| whereby contact 84 is heldfirmly against contact 86. Engagement of movable contact 95 withstationary contact 91 energizes the field winding 28 of the motor 23 bythe following circuit: line 98, wire I29, relay switch arm 9|, contacts95 and 91, wire I28, limit switch contacts 61 and 66, wire I26, fieldwinding 28, wire I23 and wire I24 to line 99. Energization of fieldwinding 28 rotates rotor 29 and therefore shafts 38 and 33 in aclockwise direction as viewed from the left in Fig. 4. Rotation of shaft33 in this manner begins to close valve 38 and also moves arm 52 towardthe right-hand end of resistance 54. This movement of arm 52 slowlychanges the resistance in shunt with solenoid windings 15 and 16 untilthe voltage drops across these solenoids are again substantially equal.When the voltage drops across solenoid windings 15 and 16 have been thusequalized, both of these solenoid windings will be equally energized.Plunger 11 is therefore returned to its middle or central position asshown in Fig. 4, and flexible switch arm 18 is returned to its normalposition and disengages movable contact its normal middle position andrender the ap- 84 from stationary contact 88. The force required tobreak contacts 84 and 86 is insuflicient 'to cause the spring I9 to pullcontacts 85 and 81 into engagement. Separation of contact. 84 from 88again equalizes the voltage drops across relay windings 88 and 89-sothat plunger 98 is returned to its central position and relay switch arm9I moves contact 95 out of engagement with contact 91 to de-energizefield winding 28 of motor 23.

If the temperature to which bimetallic element I4 responds continues toincrease, movable member I3 will move further along control resistanceI2 toward the left end thereof, and will again unbalance the voltagedrops across solenoid windings I5 and I8 as heretofore explained. Fieldwinding 28 will again be energized to operate rotor 29 to move valve 38to a more nearly closed position and to move arm 52 across balancingresistance 54 to the right until the voltage drops across solenoidwindings 15 and I8 are again rerelay winding 88 is thereby decreasedwhich re-- sults in an increased voltage drop across relay winding 89whereupon plunger 98 is moved to the right to cause contact 94 to engagecontact 98. Engagement of contact 94 with contact 96 establishes anenergizing circuit for the field winding 25 of motor 22 as follows: line98 wire I29, relay switch arm 9|, contacts 94 and 98, wire I21, limitswitch contacts 6| and 68, wire I25, field winding 25, wire I22, andwire I24 to line 99. Energization of field winding 25 causes rotor 28 torotate in a counter-clockwise direction as viewed from the left in Fig.4, which counter-clockwise rotation is imparted to shafts 38 and 33.This counterclockwise rotation of shaft 33 begins to open valve 38 andlikewise moves arm 52 across balancing resistance 54, toward the leftend thereof. When arm 52 reaches a certain position on balancingresistance 54, the voltage drops across solenoid windings I5 and I8 willbe rebalanced. Plunger II will therefore return to its middle positionand separate contact 85 from contact 81. This action will rebalance thevoltage drops across relay windings 88 and 89 and plunger 98 will moveto its central position separating contact 94 from contact 98 tode-energize field winding 25.

It will be noted that if movable member I3 should move to the extremeleft end of control resistance I2, solenoid winding I5 would be shortcircuited were it not for protective resistance I88. Solenoid winding I6would be short circuited if protective resistance I89 were omitted uponmovement of movable member I3 to the extreme righthand end of controlresistance I2. In order to rebalance the system under either of theseconditions, arm 52 would have to move to the extreme right or left endof control resistance 54 whereupon bothsolenoid windings I5 and I8 wouldbe short-circuited. This would not only be undesirable from anelectrical standpoint, but also might prevent the return of plunger IIto strip paratus inoperable. These are the reasons for includingprotective resistances I88 and I89. Protective resistance I2I likewisehas utility in protecting the maximum current flow in the energizingcircuits for relay windings 88 and 89.

From the foregoing description of the operation of Fig. 4, it will beapparent that the shaft 33 assumes a position corresponding to anyposition of movable member I3. The solenoid windings I5 and I8 may beconsidered as normally balanced electrical means which are unbalancedwhenever a movable member moves to a new position. This unbalancing ofthe normally balanced electrical means operates an electricallycontrolled device which in turn rebalances the normally balancedelectrical means and positions an instrumentality in accordance with theposition of the movable member. It will also be noted that the contacts88 and 81 remain stationary at all times and that the cooperatingcontacts 84 and 85 are first moved in one direction to complete acircuit as a result of movement of the movable member I3 and then aremoved in the opposite direction to break that circuit after aninstrumentality has been positioned in accordance withthe position ofthe movable member.

The limit switch actuators 64 and I8 may be adjustably positioned inorder to limit the extreme positions of the shaft 33 and therefore ofthe arm 52 and valve 38 or other instrumentality which it is desired tocontroL- I Referring now to Figs. 5, 6, 7, and 8, there is shown asomewhat modified embodiment of the invention. A case I38 houses a pairof induction motors I3I and I32. The motor I3l is provided with a fieldwinding I33 and a rotor I34 and the motor I32 is provided with a fieldwinding I35 and a rotor I38. Rotors I34 and I38 are both mounted on andsecured to a shaft I3'I that is suitably journalled in casing I38. ShaftI 31 is connected to a shaft I38 through a reduction gear train I39, thearrangement being such that shaft I3I drives shaft I38 at a reducedspeed in the opposite direction of rotation. The right hand end of shaftI38 extends without casing I38 and may be operatively connected to aninstrumentality which it is desired to control, such as the valve 38 ofFig. 1. The left hand extremity of shaft I38 carries a cam I48.

Case I38 supports a horizontal mounted sheet of fiber I4I. A pair ofbrackets*l42 and I42a, which are suitably secured to fiber sheet I4Inear one side thereof, support a rectangular strip I43 upon which abalancing resistance I44 is wound. A pair of similar brackets I45 andI45a support a similar strip I48 near the other side of the fiber sheetMI and in parallel relation to the I43. A cascade control resistance H1is wound about strip I46. A metal bracket I48 is secured to fiber sheetI4I between brackets I42 and I42a and has a bent-over portion I49 whichover-lies strip I43 and a similar metal bracket I58 has a bent-overportion I5I which over-lies strip I46.

A pair of guide brackets I52 and I53 are secured to fiber sheet I 4| andlie between strips I43 and I48. These guide brackets guide alongitudinally slideable fiber actuator I54 to which is" secured a pairof conducting spring fingers I55, one of whichengages balancingresistance I44 and the other of which engages the bent-over portion I49of bracket I48. A second similar pair of, conducting spring fingers I56similarly engage cascade resistance I41 and the Fiber sheet I4I alsosupports a pair of contact carrying springs I51 and I58 which carrylimit 'contacts I59 and I59c respectively. A pair of similar contactcarrying springs I60 and I6I carry limit switch contacts I62 and I63.Actuator I54 is provided with a limit switch actuator I64 which extendslaterally from actuator I54 and then to the right as viewed in Fig. 6. Asimilar limit switch actuator I65 extends laterally from the other sideof actuator I54.

A coiled spring I66 has one end secured to the right hand end ofactuator I54 and its other end is secured to fiber sheet I4I as shown atI61. The end .of limit switch actuator I64 abuts a roller I68 which ispivoted to one end of an arm I69, the other end of which is pivoted onfiber sheet I4I at I10. Arm I69 is provided with an adjustable screw III which engages an actuating arm I12 that is pivoted at I13 and carriesa pivoted roller I14 which abuts cam M6. The coiled spring I66 maintainslimit switch actuator I64, arm I69, actuating arm I12, and cam I46 inproper abutting relationship, one to another.

When shaft I36 is rotated counter-clockwise, as viewed from the left inFig. 6, actuator I54 is moved to the left by cam I40 against the actionof spring I66 and spring fingers I55 and I56 move along resistances I44and I41 respectively and the bent-over portions I49 and I5I respectivelyof brackets I48 and I50; Extreme counter-clockwise movement of shaft I38will move actuator I54 to the left until limit switch actuator I64engages contact carrying spring I51 and moves contact I59 out ofengagement with contact I59a. When shaft I38 rotates in a clockwisedirection, actuator I54 moves to the right under the action of coiledspring I66 and upon reaching an extreme right hand position, limitswitch actuator I65 engages contact carrying spring I60 and movescontact I62 out of engagement with contact I63.

From the foregoing description, it will be apparent that the device ofFigs. 5, 6, and 7 differs in certain respects from the device of Figs.1,- 2, and 3 and particularly in that the former provides straight linebalancing and cascade resistances and potentiometer operation whereasthe latter provides no cascade potentiometer and a circular or rotarybalancing potentiometer action.

Now referring to Fig. 8, a. complete. system utilizing'the apparatus ofFigs. 5, 6, and 7 is shown. This systemincludes a. control potentiometercomprising a movable member I14 which is controlled by a bimetallicelement I15" and sweeps across a control resistance I16. The systemlikewise includes a center-tapped solenoid comprisingsolenoidwindingsI11 and I18. Solenoid windings I11 and I18 control a plunger I19 whichis connected to a flexible switch .arm I by a light spring I8I. Flexibleswitch arm 'I8I carries contacts I82 and I83 which cooperate withstationary contacts I84 and I85. A'relay comprises relay windings I86and I 81 which control a. plunger I88 that is connected to a flexiblerelay switch arm I89 by a light spring I90. Relay swich arm I89 carriescontacts I9I and I92 which cooperate with stationary contacts I93 andI94.

Line wires I95 and I96 supply power to the system and the primary I91oi. a step-down transformer having a. secondary I98 is connected to linewires I95 and I96. Wires I99 and 200 connect one side of secondary I98with the free end of solenoid winding I11 and wires 2M and 202 connectthe other side of secondary I98 with the free end of solenoid windingI18. Wire 203 conects wire 200 with one end of a protective resistance204'. Wires 205, 206, and 201 interconnect the other end of protectiveresistance 204, one end of control resistance I16 and one end ofbalancing resistance I44. One end of a protective resistance 208 isconnected to. wire 202 by a wire 209. Wires 2 I0,'

21 I, and 2I2 interconnect the other end of protective resistance 208,the other end of control resistance I16 and the other end of balancingresistance I44. Wires 2I3, 2I4, and 2 I5 interconnect movable memberI14, the junction of solenoid windings I11 and I18 and spring fingersI55, the latter by virtue of their sliding contact with bracket I 48.

A. wire 2I6 connects contact I84 with a small number of turns ofsolenoid winding I11 and a wire 2I1 similarly connects contact I with asmall number of turns of solenoid winding I18. Wires 2I8 and H9 connectflexible switch arm I86, a protective resistance 220, and the junctionof relay windings I86 and I81 in series. Wire 22I connects the outer endof relay winding I86 with one side of secondary I98 through wire 20I anda wire 222 similarly connects the outer end of relay winding I81 withthe other side of secondary I98 through wire I99.

'A wire 223 connects line I and relay switch arm I89. A wire 224connects contact I94 to contact I59 and a wire 225 connects contact I93with contact I62. Contacts I59a and I63 are respectively connected toone side of field windings I35 and I33 by wires 226 and 221 and theother sides of these field windings are connected to line I96 by a wire228.

Operation of the system of Fig. 8

The operation of the system of Fig. 8 is similar to the operation of thesystem of Fig. 4 in its broader aspects. With the parts in the positionshownin Fig. 8, the movable member I14 is in engagement with the centralportion of control resistance I16 and the spring fingers I55 are inengagement with the central portion of balancing resistance I44 andmember I48. With the parts in these positions the voltage drop acrosssolenoid winding I11 is equal to the voltage drop across the solenoidwinding I18 which results in 'equal energization of these solenoidwindings.

following circuit: secondary I96, wire I99, wire 222, relay windingsI81, and I86, wire 22I, and wire 20I to the other side of secondary I98.This equal energization of relay windings I86 and I81 positions plungerI88 in a central position. Flexible relay switch arm I89 thereforeassumes its normal unflexed position in which contacts I9I I93 and I94.Field windings I33 and I35 are both de-energized and shafts I31 and I38are stationary. The position of shaft I38 corresponds to the position ofmovable member I14.

If the temperature to which bimetallic element I15 responds now rises,movable member I14 will .be moved along control resistance I16 towardthe left end thereof. Such movement of movable member I14 changes theresistances '06 and I92 are out of engagement with contacts associatedwith solenoid windings I 11 and I18 in such a manner that the voltagedrop across solenoid winding I18 becomes greater than the voltagedrop'across solenoid winding I11. Solenoid winding I18 is thereforeenergized to a greater degree than solenoid winding I11 and plunger I19is moved to the right resulting in engagement of contact I83 withcontact I85. En-

' gagement of contact I83 with contact I85 connects protectiveresistance 228 in series with a small number of turns of solenoidwinding I18, and they in turn are connected in parallel with relaywinding I85. The results are two-fold. First, the voltage drop acrossrelay winding I81 becomes greater than that across relay winding I85whereupon plunger I88 moves to the right and causes contact I9I toengage contact I93. Second, the current traversing the small number ofturns of solenoid winding I18 exerts an additional force tending to moveplunger I19 to the right, whereby contact I83 is held in firm engagementwith contact I85.

Engagement of contact I9I with contact I93 establishes an energizingcircuit for field winding I33 as follows: line I95, wire 223, relayswitch arm I89, contacts I9I and I93, wire 225, limit contacts I52 andI53, wire 221, field rWinding I33, and wire 228 to line I98.Energization of field winding I33 rotates rotor I34 in acounterclockwise direction, as viewed from the left in Fig. 8, whereuponshaft I38 is rotated in a clockwise direction by the reduction geartrain I39 (it being remembered that the reduction gear train I39 impartsan opposite direction of rotation to shaft I38 in respect to thedirection of rotation of shaft I31). Clockwise rotation of shaft I38allows actuator I54 to move toward the right whereupon spring fingers I55 move along balancing resistance I44 and member I48 toward the righthand extremities thereof. Spring fingers I55 continue to move in thisdirection until the resistances associated with solenoid windings I11and I18 have been readjusted to such an extent that the voltage dropsacross solenoid windings I11 and 'I18 are again equal. When thesevoltage drops have been equalized in this manner, plunger I19 returns toits central position and contact I83 is moved out of engagement withcontact I85. Separation of contacts I83 and I85 equalized the voltagedrops across relay windings I85 and I81 and contact I9I moves out ofengagement with contact I93 whereupon the circuit through field windingI33 is interrupted. The position of shaft I38 now corresponds to the newposition of movable member I14.

If the temperature to which bimetallic element I15 continues to rise,the above described action will be repeated. If the temperature to whichbimetallic element I15 should fall, the opposite action will take place,i. e., contact I82 will engage contact I84 which will result inengagement-of contact I92 with contact I94 followed by energization offield winding I85 which will cause rotation of shaft I38 in acounterclockwise direction.

From the foregoing description of the opera-.

tion of Fig. 8, it will be apparent that this operation is very similarto the operation of Fig. 4. Extreme movements of shaft I38 in eitherdirection are prevented by limit switch contacts I52 and I53 or I58 andIBM. The resistance I41 and the member I58 may be used as a controlpotentiometer for another similar apparatus whereby a second shaft maybe positioned in The movement of shaft I38 may be utilized to controlany desired instrumentality valve 38 in Fig. 1.

Where the work required of the feversible motors is relativelylight,'they may be replaced by motors having low voltage windings. Insuch a case, the relay comprising windings I85 and I81 may be omitted orthe windings I85 and I81 may replace the motor field windings I33 andI35.

Turning now to Fig. 9, it will be noticed that the system therein shownincludes the equivalent of the system shown in Fig. 8. Similar parts inFig. 9 have been referenced to'correspond with the like parts of Fig. 8.

Assuming that the shaft I38 controls a-valve in the fuel line of afurnace and that bimetallic element I15 responds to the furnacetemperature, the valve controlled by shaft I38 will be moved topositions corresponding tothe temperature of bimetallic element I15 inthe manner heretofore described for Figs. and 8. With the parts in theposition shown, the valve will be subsuch as the stantially half openand the furnace temperature is at the desired point. If the furnace isoperating under a small load, the temperature thereof will rise with theresult that bimetallic element I15 will move movable member I14 alongcontrol resistance I15 toward the left hand end thereof which actionwill partially close the valve controlled by shaft I38 until abalance'is reached wherein the heat input maintains the furnace at aneven temperature as described in connection with Fig. 8. Thistemperature, however, is somewhat higher than that desired as evidencedby movement of movable member I14 to the left of its centerposition. Thefurnace temperature can be maintained fairly close to the desired pointby making the over-all length of control resistance I15 correspond toarelatively small. temperature differential in the furnace. However, ifthe over-all length of control resistance I15 is made to correspond to avery small furnace temperature differential in an attempt to maintainthe furnace temperature within very narrow limits, such as are sometimesrequired in commercial processes, there may be a resultant hunting ofthe valve controlled by the shaft I38 and the system may no longermodulate or proportion the position of the valve controlled by shaftI38. As a result, when it is desired to control the furnace temperaturedifferential within very narrow limits under varying load conditions, itis necessary to provide additional mechanism wherebythe position of thevalve and shaft I38 may be adjusted automatically in accordance with thedeparture of the furnace temperature from normal and/or in accordancewith the length of time that such a departure persists and/or uponinitial reverse changes in furnace temperature. The additional mechanismshown in Fig. 9 makes this automatic adjustment possible.

Comparing Fig. 9 with Fig. 8, it will be noted that the fixed protectiveresistance 284 of Fig. 8 is not found in Fig. 9. However, a resistance229 has one end thereof connected to wire 288 and solenoid winding I11by a wire 238. A rotatable contact finger 23I which is fixed to a shaft232 is connected to wires 285 and 281 by a wire 233. The contact finger23I and resistance 229 constitute an adjustable resistance or rheostatwhich takes the place of the fixed protective resistance 284 of Fig. 8.Likewise, the fixed protective resistance 288 of Fig. 8 is replaced by aresistwire 235, resistance 234, contact finger 236, and wire 231.

The wire 205 is connected to wire 283 through a manually adjustablerheostat comprising a resistance 238 and a manually operable contactfinger 23811. The contact finger 238a and resistance 238 comprise asensitivity control for balancing resistance H82 and its function willbe hereinafter described.

The wire 2113 is similarly connected to wire 2% through a rheostatcomprising a resistance 289 and a manually adjustable contact finger2353a. This manually adjustable rheostat comprises a sensitivity controlfor control resistance M and its function will be referred to later inthis description.

The shaft 232 carries a ratchet wheel 242 and a pinion 223. Pinion 243meshes with an idler gear 224 which in turn meshes with a second pinion225 mounted upon a shaft 226. Shaft 246 carries a second ratchet wheel281. Line wires 248 and 249 constantly energize the field winding 258 ofa timing motor generally indicated at 255, wires 252 and 253 connectingline wires 248 and 249 to the opposite ends of field winding 258. Therotor 25d of the timing motor 250 drives a reduction gearing hereinshown as a worm 255 and a worm wheel 255. A crank pin 251 is carried byworm wheel 258 and the free end of crank pin 251 extends into a slot 258which is formed in a lever 259, one end of which is pivoted as shown at268. A vertical actuator 262 has one of its ends pivoted to the free endof" the lever 259 as shown at 262. The actuator 28H is constantlyreciprocated vertically by the timing motor 25I and associated mechanismand when the actuator 26K! is positioned substantially vertically itreciprocates freely without engaging either of the ratchet wheels 242and 241. If the lower free end of actuator 26I is moved to the left, itengages the teeth of ratchet wheel 242 upon upward movement so as torotate shaft 232 and shaft 246 through pinions 243 and 245 and idlergear 244 in a counterclockwise direction as viewed from the right inFig. 9. Likewise, if the lower end of actuator 26I is moved to theright, it engages the teeth of ratchet wheel 241 during its upwardmovements and rotates shafts 246 and 232 in a clockwise direction.

The position of actuator 26I is controlled by a plunger 263 to which itis connected by a link 264 and spring 265. The plunger 263 is controlledby a pair or solenoid windings 266 and 261 which have adjacent endsinterconnected and their free ends connected to the secondary 268 of atransformer by wires 269 and 218. The primary 2" of the transformer isconstantly energized by line i A rotatable contactwires 218 and 211. Theother end of corrector resistance 212 is connected to wire 218 andsolenoid winding 261 through a protective resistance 218 by wires 219and 288. Movable member 213 is connected by a wire 28I to a manuallyoperable contact finger 282 which may be moved across a resistance 283,one end of which is connected to the junction of solenoid windings 266and 261 by a wire 284. Contact finger 282 and resistance 263 comprisethe sensitivity control for the corrective mechanism and its functionwill be described under Operation. v

The shaft 246 may control a corrector indicating potentiometercomprising a movable contact finger 285 and resistance 288 which controlsolenoid windings 281 and 288 that in turn position an indicating needle289. The solenoid windings 281 and 288 and the corrector indicatingpotentiometer are connected together through suitable protectiveresistances and are also connected to the secondary 268 in the mannerpreviously set forth in respect to similar arrangements.

The movable member N4 of Fig. 9 not-only engages control resistance l16but also extends therebelow and carries apair of contacts 248 and 24Hwhich are adapted, upon reverse movements of movable member I14, torespectively engage contacts 298 and 29I. Contacts 298 and 29 I arecarried by a plate 292 which is herein shown, for convenience ofillustration, as being pivoted at a point indicated at 292a. The pivotalmounting of plate 292 comprises any well known type of frictionalarrangement whereby the plate 292 remains in any position to which it ismoved. In actual practise, the plate 292 is pivoted concentrically withthe center of movement of the movable member. I14 in order that contacts248, 24I, 298 and 29I will retain their proper alignment.

A rheostat comprises a resistance 293 and a manually adjustable contactfinger 293a. One end of resistance 293 is connected to wire 233 and thecontact finger 293a is connected to contact 29I by a wire 294. A similarrheostat comprises a resistance 295 and manually adjustable contactfinger 295a. The resistance 295 is connected to wire 235 and the contactfinger 295a is connected to contact 298 by a wire 296.

Operation of the system of Fig. 9

With the parts in the position shown in Fig. 9, the valve controlled byshaft I36 is, for instance, in half -open position, the temperature ofthe furnace is at the desired point with the result that movable memberI14 is contacting the central portion of control resistance I16,contacts 248 and MI are out of engagement with contacts 298 and 29Irespectively and the movable member 213 is contacting the center portionof corrector resistance 212. Field windings I33 and I35 are thereforeboth de-energized as heretofore explained in connection with Fig. 8 andthe actuator 26I is in a. vertical position wherein it is reciprocatedby timing motor 25I without engaging either of the ratchet wheels 242 or241.

If the temperature of the furnace should rise, bimetallic element I15will move movable member I14 along control resistance I16 bringingcontact 2 into engagement with contact 29I. Engagement of contacts 24Iand 29I places that part of resistance 293 which is between wire 233 andcontact finger293a in parallel with the left hand portion of controlresistance I16, therebydecreasing the voltage drop across solenoidwinding I11 a predetermined amount which is dependent upon drop acrosssolenoid winding I18 is increased and the resulting unequalenergizations of solenoid windings I11 and I18 causes plunger I19 tomove to the right with the result that field winding I33 is energized torotate shaft I38 in a clockwise direction as viewed from the left inFig. 9. Such rotation of shaft I38 begins to close the valve controlledthereby and begins to move spring fingers I to the right along balancingresistance I44 and member I48. Spring fingers I55 must not only movealong balancing resistance I44 enough to balance the effect of the newposition of movable member I14 on control resistance I12 but must alsomove an extra amount sufficient to overcome the unbalancing resultingfrom the engagement of contacts 2 and 29I. In this manner, the initialmovement of movable member I14 to the left resulted in an initialrelatively large adjustment of the valve in addition to that adjustmentresulting from the movement of the movable member to a new position onits control resistance.

This movement of bimetallic element I15 has also moved movable member213 to the left along resistance 212 whereupon the voltage drop acrosssolenoid winding 261 is made greater than the voltage drop acrosssolenoid winding 266 and plunger 263 moves to the right. This actionmoves the lower free end of actuator 26I to the right and when actuator26I is next raised by timing motor 25I and the associated mechanism,ratchet wheel 241 is moved in a clockwise direction as viewed from theright. Shaft 232 is therefore likewise rotated-in a clockwise directionwith the result that the resistance of the circuit comprising wire 238,resistance 229, contact finger 23I, and wire 233 is decreased and theresistance of the circuit comprising wire 235, resistance 234, contactfinger 236, and wire 231 is increased. This change in resistances ofthese circuits again unequalizes the voltage drops across solenoidwindings I18 and, I11 whereby solenoid winding I18 is again energized toa greater degree than solenoid winding I11. Plunger I19 therefore againmoves to the right and results in a further energization of fieldwinding I33 whereupon shaft I38 again rotates in clockwise directionasviewed from the left. This action closes the valve controlled by shaftI38 to a greater degree and likewise moves spring fingers I55 closer tothe right hand end of glancing resistance I44 to again rebalance thevoltagedrops across solenoid windings I11 and I18 whereupon fieldwinding I33 is again de-energized.

The shaft 232 will be intermittently rotated in a clockwise directioneach time the actuator 26I is raised until the furnace temperature hasreturned to normal and movable member 213 is brought back to theposition shown in Fig. 9. The angular rotation .of shaft 232 each timeactuator 26I is raised depends upon the amount of displacementof thelower free end of actuator 26I away from vertical and toward the'rightwhich in turn is dependent upon the deviation of the furnace temperaturefrom normal as indicated by the position of movable member 213. Thecorrective movements of the valve toward closed position are thereforemade in accordance with the departure of the furnace temperature fromnormal, and in accordance with the length of time such departurepersists. The time factor is by virtue of the timing motor 25I whichreciprocates actuator 26I preferably at the rate of a complete up anddown movement every two minutes.

Continued rise in furnace temperature resulting in further movement ofmovable member I14 along control resistance I16 rotates plate 292 aboutits pivot 292a. Such further movement also again unbalances the voltagedrops across solenoid windings I11 and I18 resulting in fur ther closingof the valve. Continued rise in furnace temperature also moves movablemember 213 further along corrector resistance 212 whereby the voltagedrop across solenoid winding 261 is further increased and the voltagedrop across solenoid winding 266 is further decreased. Plunger 263therefore moves further towards the right and each subsequent upwardmovement of actuator 26I will rotate shaft 232 in a clockwise directiona larger amount than formerly, whereby increased amounts of correctionwill be applied to the system.

The various closing movements thus supplied to the valve will check therise in furnace temperature but as long as the furnace temperatureremains away from the normal desired value, further corrective movementswill be applied. Finally the furnace temperature will; begin to lower.Initial lowering of the furnace temperature will cause movable memberI14 to disengage contact 24l from contact 29I thereby removing theresistance 293 from its parallel relationship with left-hand portion ofthe control resistance I 16. The voltage drop across solenoid windingI11 will thereupon be increased and the voltage drop across solenoidcoil I18 will be similarly decreased. As a result, field coil I35 willbe energized to give the valve an initial opening movement. A slightfurther movement of control member I14 to the right in response to afurther drop in furnace temperature will cause contact 24ll to engagecontact 290, whereby resistance 295 is placed in parallel with the righthand portion of control resistance I16 which again increases the voltagedrop across solenoid winding I11 and decreases the voltage drop acrosssolenoid winding I18, resulting in a further initial opening of thevalve. In this manner, a small fall infurnace temperature results in aninitial relatively large opening movement of the valve.

If the furnace temperature continues to fall until the desired normal isreached, the voltage drops across solenoid windings 266 and 261 will berebalanced and the actuator 26I returned to its vertical positionwherein it. does not engage either of the ratchet wheels 242 or 241 andfurther corrective movements due to a departure from normal will nolonger be applied.

The movement of control member I14 to the right along control resistanceI16 also increases the voltage drop across solenoid winding I11 anddecreases the voltage drop across solenoid winding I18 to open the valvean amount corresponding to the movement of the movable member I14.

If the furnace temperature falls below the desired normal, movablemember 213 will be moved to the right of the center of correctorresistance 212 resulting in a greater voltage drop across solenoidwinding 266 than across solenoid winding 261 and actuator 26I will bemoved to the left of its vertical position. Actuator 26I will thereafterengage the teeth of ratchet .wheel 242 upon each of its upward movementsand shaft 232 will thereupon be rotated in a counter-clockwisedirection, when looking from the right in Fig. 9 to intermittentlyincrease the amount of resistance 229 and decrease the amount ofresistance 234. Thus the valve is given intermittent opening movementsin an effort to restore the furnace temperature to normal as long as itremains below normal.

Whenever the furnace temperature becomes normal so that movable memberI14 again contacts the center of control resistance I16 and the' movablemember 213 contacts the center of corrector resistance 212, all furthercorrective movements of the valve will cease. However, the valve is notnecessarily in its midposition since it may be displaced therefrom ineither direction, depending upon the position which contact fingers 23Iand 236 areleft in respect to their respective resistances 229 and 234and also depending on whether or not either of contacts 240 or 24I is inengagement with its respective contact 290 or 23I Such new position ofthe valve should exactly balance the new load condition imposed on thefurnace.

From the foregoing description of the opera= tion of the apparatus ofFig. 9, it will be apparent that this modification provides for thepositioning of an instrumentality to be controlled in accordance withfour difierent factors. First, the instrumentality is primarilypositioned in accordance with the movements of a movable member. Second,the instrumentality is given a quick initial movement whenever themovement of the movable member reverses. Third, the instrumentality ispositioned in accordance with the degree of departure of the movablemember from its desired normal position. And fourth, the instrumentalityis positioned in accordance with the length of time such departurepersists.

As previously stated, in this specific embodiment of the invention, aspeed of two minutes has '49 been found suitable for a completerevolution of for reasons of clarifying the explanation, but in actualoperation these movements will all overlap and occur simultaneously to agreat extent.

The system of Fig. 9 includes several adjustments by reason of which theapparatus may be easily adapted to control any one of a number ofdifferent devices. If the contact finger 233a is rotatedcounter-clockwise to exclude more of the resistance 239 from thecircuit, then a smaller movement of movable member l 14 along controlresistance 010 will be required to unbalance the voltage drops acrosssolenoids Il and i773 sufficiently to move one of the contacts 632 andI83 into engagement with its respective contact til -l or I85. In thismanner, a smaller temperature change is necessary to obtain a givenmovement of the instrumentality to be controlled. Movement of contactfinger 239a in a clockwise direction, on the other hand, decreases thesensitivity of the system. In a like manner, movement of contact finger23811 in a clockwise direction decreases the amount of resistance 238 incircuit with balancing resistance I44 with the result that the voltagedrops across solenoid windingsl'll and I 18 are rebalanced upon asmaller movement 144. In this manner, a smaller movement of theinstrumentality to be controlled will result upon a given movement ofmovable member I14. Likewise, larger movements of the instrumentality tobe'controlled will result for a given movement of movable member I14 ifcontact finger zaaa is rotated along resistance 238 in acounterclockwise direction. By means of these two adjustments, theresponse of the system of Fig. 9 may be varied as desired or necessaryin order to obtain the desired control. These two adjustments areequally applicable to the systems of Figs. 4 and 8 and to the remainingsystems to be hereinafter described.

Rotation of contact finger 282 in a clockwise direction places more ofresistance 283 in circuit with the corrector potentiometer and solenoids260 and 261 with the result that the movement of plunger 263 will bedecreased for a given movement of movable member 213. Counter-clockwiserotation of contact finger 282 will similarly decrease the amount ofmovement of movable member 213 required to move plunger 253 a givenamount, adjustment of contact finger 2 02 therefore determines theamount that actuator 26I will be displaced from vertical upon a givendeviation of the furnace temperature from normal with the result thatthe amount of corrective adjustment applied to the system in apredetermined time for a predetermined variation from normal may bevaried as desired.

Adjustment of contact fingers 293a and 295a along their respectiveresistances 293 and 295 determines the amount of resistance placed inand out of circuit with the left and right hand portions of controlresistance I16 upon making and breaking of contacts MI and H and 240 and230 respectively, whereby the magnitude of the initial adjustment givento the instrumentality to be controlled upon reverse movements ofmovable member I14 may be varied at will.

While the system of Fig. 9 has been specifically described ascontrolling the flow of fuel to a fur nace which it is desired tomaintain at a constant temperature under various load conditions, itwill be appreciated that such a system has a great degree of utility inmany other fields.

Fig. 10 shows a system which includes some modifications and additionsover the system of Fig. 8 although the fundamentals of operation of thetwo systems are very similar. The solenoid windings I11 and I18 andmechanism controlled thereby, the relay windings I86 and I81 andmechanism controlled thereby, and the interconnecting circuits for thesesolenoid and relay windings are the same as in Fig. 8 and have beensimilarly referenced. Fig. 10 likewise includes the balancing resistanceI44, member MB- and spring fingers I55 of Fig. 8.

One end of balancing resistance I44 is connected to the outer end ofsolenoid winding I11 through a protective resistance 300 by means ofwires I, 302, and 303. Similarly, the other end of balancing resistanceMt is connected to the outer end of solenoid winding I18 through aprotective resistance 304 by means of wires 305, 306, and 301. Themember I48 is connected to the junction of solenoid windings I11 and-I18 by means of wires 308 and 303. g

The junction of wires 302 and 303 is connected to a movable contactfinger 3'I0 by a wire 3| I.

Contact finger 3| 0 engages a resistance 3I2. The junction of wires 300and 301 is connected to a movable contact finger 3I3 by a wire 3M andcontact finger 3I3 engages a resistance 3I5. The junction of wires 338and 303 is connectedto a contact finger 316 by means of a wire 311 andcontact finger 316 engages a resistance 318. Contact fingers 318, 313,and 316 are all simultaneously controlled by a rod 319 which is hereinshown as operated by the bellows motor 328, of a fluid-thermostat havinga controlling element 321. The controlling element 321 may respond, forexample, to outdoor temperatures. Upon a rise in outdoor temperature,the three contact fingers 318, 313, and 316 are rotated in acounterclockwise direction and upon a fall-in outdoor temperature, theyare rotated in a clockwise direction.

The single control resistance 116 and the single movablemember 114 ofFig. 8 are replaced by a plurality of resistances, which areinterconnected in a manner to be hereinafter explained, and by aplurality of movable members. Movable members 322 and 322a are connectedby a link 323 which is controlled by an actuator 324 that is hereinshown as a thermostatic element. Movable member 322 engages a resistance325 and movable member 322a engages a resistance 325a. Another set ofmovable members 326 and 326a are connected together by a link 321 whichis controlled by thermostatic element 328 and these movable membersengage resistances 329 and 329a. A third set of movable members 338 and338a are connected together by a link 331 which is actuated by athermostatic element 332. Movable members 338 and 330a respectivelycontact resistances 333 and 333a. A fourth set of movable members 334and 334a are interconnected by a link 335 which is controlled by athermostatic element 336 and these movable members respectively engageresistances 331 and 331a.

One end of resistance 312 is connected to movable member 322 by wires338 and 339. One end of resistance 325 is connected to movable member326 by a wire 340. One end of resistance 329 is connected to the middleof resistance 318 by wires 341, 342, and 343. It will therefore be seenthat portions of resistances 325 and 329 are connected in series and areconnected across solenoid winding 111 through resistance 312. The sameend of resistance 312 is connected to movable member 338 by wires 338and 344. One end of resistance 333 is connected to movable member 334 bya wire 345. One end of resistance 331 is connected to the mid-portion ofresistance 318 by wires 346, 341, and 343. Resistances 333 and 331 aretherefore similarly connected across solenoid winding 111 throughresistance 312 and are in parallel with the series resistances 325 and329. The series parallel arrangement of resistances 325, 329, 333, and331 comprise an effective resistance which replaces the left handportion of control resistance 116 of Fig. 8.

In a similar manner, one end of resistance 315 is connected to movablemember 322a by wires 348 and 349. One end of resistance 325a isconnected to movable member 326a by a'wire 358. One end of resistance329a is connected to the mid-portion of resistance 318 by wires 351,342, and 343. One end of resistance 315 is also connected to movablemember 3311a by wires 348 and 352. One end of resistance 333a isconnected to movable member 334a by a wire 353 and one end of resistance331a is connected to the center portion of resistance 318 by wires 354,341, and The series resistances 322a328a and 338a-334a are thereforeconnected in parallel across solenoid winding 118 through resistance 315and replace the right hand portion of control resistance 116 of Fig. 8.v

Neglecting resistances 312, 315,- and 318 for the time being, the abovedescribed composite resistance comprising the various series parallelcircuits have an effective resistance equal to the control resistance116 of Fig. 8. Now if actuators 324, 328, 332, and 336 were all similarand responded to the same temperatures, the system of Fig. 10 wouldoperate exactly the same as the system of Fig. 8. These four actuators,however, are made to respond to different temperatures, for example byplacing them in different rooms of a house or building, with the resultthat the unbalancing of the voltage drops across solenoid windings 111and 118 is dependent upon or influenced by the various temperatures towhich each and every actuator responds whereby the position of plunger119 is not controlled by any single actuator, but is controlled by thecooperation of ,all of the actuators. The number of actuators andmovable members controlled thereby may be varied as desired and theinterconnection of the various resistances contacted by the movablemembers may be arranged in any desired manner so that the voltage dropsacross solenoid windings 111 and 118 are controlled as the result ofchanges of temperature or any other condition or force as may berequired in order to properly control any desired system or process.

If the temperature to which element 321 responds should rise, the amountof resistance 312 which is connected in circuit with the system isreduced and the amount of resistance 315 which is connected in circuitwith the system is increased with the result that the voltage dropsacross solenoid windings 111 and 118, as determined by the positions ofactuators 324, 328, 332, and 336, is modified. The shaft 138 may controla steam valve or a fuel supply valve by which the various rooms in thebuilding or house are heated and therefore changes in the outdoortemperature to which element 321 responds will modify the position ofsuch a valve as determined by the temperatures in the various rooms.

It will be noted that equal amounts of resistance 318 are placed incircuit with the junction of solenoid windings 111 and 118 and themember 148 upon movement of rod 316 in either direction and that theamount of resistance 318 thus put in circuit is proportionate to themovement of rod 319 from its normal position in which contact finger 316engages the mid-portion of resistance 318. The resistance 318 might betermed an automatic adjustable protective resistance which functions toplace varying amounts of protective resistance in the system wheneverrod 319 is moved away from its normal position. This adjustableprotective resistance is placed in circuit in the system in order toprevent full secondary voltage from being placed across either of thesolenoid 4 stood that the various actuators may respond to condit onsother than temperature and that the rod 319 may be positioned bytemperatures other than outdoor temperature or by any other desiredcondition or force.

The system of Fig. 10 has been herein shown

